Dr Fullilove explained that the presidency of Roosevelt had fascinated him even before he wrote his Masters thesis on it while studying as a Rhodes scholar at Oxford in the late 1990s. He said while writing the thesis on President Roosevelt he was able to “get inside his head”, partly by visiting his personal library at his house in upstate New York, a couple of hours north of Manhattan.

“I was able to look at his papers as president that he signed and to look at all his diary notes and everything and just get inside the head of someone I had always admired.” After completion of the Masters and his return to Australia, his supervisors at Oxford encouraged him to upgrade the Masters to a PhD, a project he finally began three years later.

When the PhD was finished he began to write widely on international affairs, being published regularly in many leading publications including The Sydney Morning Herald, The Australian, The Australian Financial Review, The New York Times, The Financial Times,The Washington Post, The Daily Beast, The National Interest and Foreign Affairs. After spending almost a decade as director of the Lowy Institute’s global issues program he was appointed as the Institute’s executive director.

And so when he signed up with a literary agent in 2009 he considered writing books on various topics but kept coming back to Roosevelt.

“A lesson I have learnt in life,” he told Warrane residents, “is that if you do the things that interest you are likely to do the best you can.”

He said he had written about Roosevelt first of all because he wanted to write about the President he had always admired.

“I had the view and still have the view that FDR was the most important statesman of the 20th century,” he said. “He saved America from the Great Depression. He led the allies to victory over dictators. He won four consecutive presidential elections … and he did it with a broken body.

He was someone who was paralysed with polio at about my age at a time when we were much less forgiving and understanding about disability than we are today.”

Dr Fullilove said Roosevelt was a “seductive and effervescent” character.

“This matters when you spend years studying somebody,” he said. “Winston Churchill said that meeting FDR for the first time was like opening your first bottle of champagne. “And when you write about someone over the course of years it is like having breakfast, lunch and dinner with them. They come to inhabit a part of your brain, a part of your life.”

While he admired people who wrote biographies about Joseph Stalin and Adolph Hitler, Dr Fullilove said he personally couldn’t do it because it would be too gloomy.

The second reason he wrote the book was that he believed the period before the start of the Second World War and American entry into the war was the turning point of the 20th century.

He said while this was a big claim, he made it because in this period the “disposition of forces” in the world changed with the forming of the axis of power between the United States, Britain and the Soviet Union. But America itself had also changed.

“It was transformed during this period from a nervous, isolationist power with the 19th largest army in the world, just creeping in to the top 20 armies in the world, into a global leader… and we are still living in the American century that really started in this period.”

Roosevelt had a struggle to get Americans, of whom only one in 40 were in favour of entering the war, to change their minds.

“I was interested in how a country as big and diverse and difficult and rancorous and isolated as the United States could turn so quickly. How could Roosevelt, trapped in a wheelchair in Washington, distrustful of many of his ambassadors, distrustful of the State Department, how could he come to have faith in the ability of Churchill’s Britain to withstand the German attacks, in the ability of Stalin to stand up to his former ally?”

The third reason he had wanted to write the book was that he wanted to write about the kind of history he liked to read, which was not history about vast impersonal forces, but about individuals and their interplay with these forces.

Because Roosevelt could not depend on his own diplomats he had to turn to five associates - “remarkable and often remarkably weird individuals” who he sent on missions to Europe.

After sharing some observations on each of the five individuals who played such a big role in the entry of the United States into the War, Mr Fullilove made some observations on the role being played in the world today by the US.

He said he believed that the US now had an “unbalanced investment portfolio”, directing too much of its attention to the Middle East and not enough towards Asia, and particularly towards China which would probably be the biggest economy in the world by 2015.

The security news in the Asian region had been troubling in recent times, particularly due to trends in North Korea. If Washington did not reassure its Asian allies that it is in the region to stay, then countries like Japan could take matters into their own hands and that presented the possibility for “escalation”.

“I think that having the Americans here makes sense,” he said. “It makes strategic sense to them and it is good for us.

“And here’s the thing: it takes enormous effort to pivot a country - as I began - as big, as rancorous as the United States. And you are starting to see that now: on the front page of The Australian today was a big story on the Inspector General of the State Department criticising the pivot and saying that there wasn’t enough meat in the sandwich - it was all hat and no cattle, if you like.

“You now have a secretary of State, John Kerry, who is much more interested in bringing peace to the Holy Land than he is to deeply engaging in Asia…”

During a lively question-and-answer session Dr Fullilove discussed a wide range of international political and security issues, including the role of the G20 and the need for bolstering its influence.